import { Checksum, SourceData } from "@smithy/types";
import { fromUtf8 } from "@smithy/util-utf8";

import { BLOCK_SIZE, DIGEST_LENGTH, INIT } from "./constants";

/**
 * @internal
 */
export class Md5 implements Checksum {
  private state!: Uint32Array;
  private buffer!: DataView;
  private bufferLength!: number;
  private bytesHashed!: number;
  private finished!: boolean;

  constructor() {
    this.reset();
  }

  update(sourceData: SourceData): void {
    if (isEmptyData(sourceData)) {
      return;
    } else if (this.finished) {
      throw new Error("Attempted to update an already finished hash.");
    }

    const data = convertToBuffer(sourceData);

    let position = 0;
    let { byteLength } = data;
    this.bytesHashed += byteLength;

    while (byteLength > 0) {
      this.buffer.setUint8(this.bufferLength++, data[position++]);
      byteLength--;

      if (this.bufferLength === BLOCK_SIZE) {
        this.hashBuffer();
        this.bufferLength = 0;
      }
    }
  }

  async digest(): Promise<Uint8Array> {
    if (!this.finished) {
      const { buffer, bufferLength: undecoratedLength, bytesHashed } = this;
      const bitsHashed = bytesHashed * 8;
      buffer.setUint8(this.bufferLength++, 0b10000000);

      // Ensure the final block has enough room for the hashed length
      if (undecoratedLength % BLOCK_SIZE >= BLOCK_SIZE - 8) {
        for (let i = this.bufferLength; i < BLOCK_SIZE; i++) {
          buffer.setUint8(i, 0);
        }
        this.hashBuffer();
        this.bufferLength = 0;
      }

      for (let i = this.bufferLength; i < BLOCK_SIZE - 8; i++) {
        buffer.setUint8(i, 0);
      }
      buffer.setUint32(BLOCK_SIZE - 8, bitsHashed >>> 0, true);
      buffer.setUint32(BLOCK_SIZE - 4, Math.floor(bitsHashed / 0x100000000), true);

      this.hashBuffer();

      this.finished = true;
    }

    const out = new DataView(new ArrayBuffer(DIGEST_LENGTH));
    for (let i = 0; i < 4; i++) {
      out.setUint32(i * 4, this.state[i], true);
    }

    return new Uint8Array(out.buffer, out.byteOffset, out.byteLength);
  }

  private hashBuffer(): void {
    const { buffer, state } = this;

    let a = state[0],
      b = state[1],
      c = state[2],
      d = state[3];

    a = ff(a, b, c, d, buffer.getUint32(0, true), 7, 0xd76aa478);
    d = ff(d, a, b, c, buffer.getUint32(4, true), 12, 0xe8c7b756);
    c = ff(c, d, a, b, buffer.getUint32(8, true), 17, 0x242070db);
    b = ff(b, c, d, a, buffer.getUint32(12, true), 22, 0xc1bdceee);
    a = ff(a, b, c, d, buffer.getUint32(16, true), 7, 0xf57c0faf);
    d = ff(d, a, b, c, buffer.getUint32(20, true), 12, 0x4787c62a);
    c = ff(c, d, a, b, buffer.getUint32(24, true), 17, 0xa8304613);
    b = ff(b, c, d, a, buffer.getUint32(28, true), 22, 0xfd469501);
    a = ff(a, b, c, d, buffer.getUint32(32, true), 7, 0x698098d8);
    d = ff(d, a, b, c, buffer.getUint32(36, true), 12, 0x8b44f7af);
    c = ff(c, d, a, b, buffer.getUint32(40, true), 17, 0xffff5bb1);
    b = ff(b, c, d, a, buffer.getUint32(44, true), 22, 0x895cd7be);
    a = ff(a, b, c, d, buffer.getUint32(48, true), 7, 0x6b901122);
    d = ff(d, a, b, c, buffer.getUint32(52, true), 12, 0xfd987193);
    c = ff(c, d, a, b, buffer.getUint32(56, true), 17, 0xa679438e);
    b = ff(b, c, d, a, buffer.getUint32(60, true), 22, 0x49b40821);

    a = gg(a, b, c, d, buffer.getUint32(4, true), 5, 0xf61e2562);
    d = gg(d, a, b, c, buffer.getUint32(24, true), 9, 0xc040b340);
    c = gg(c, d, a, b, buffer.getUint32(44, true), 14, 0x265e5a51);
    b = gg(b, c, d, a, buffer.getUint32(0, true), 20, 0xe9b6c7aa);
    a = gg(a, b, c, d, buffer.getUint32(20, true), 5, 0xd62f105d);
    d = gg(d, a, b, c, buffer.getUint32(40, true), 9, 0x02441453);
    c = gg(c, d, a, b, buffer.getUint32(60, true), 14, 0xd8a1e681);
    b = gg(b, c, d, a, buffer.getUint32(16, true), 20, 0xe7d3fbc8);
    a = gg(a, b, c, d, buffer.getUint32(36, true), 5, 0x21e1cde6);
    d = gg(d, a, b, c, buffer.getUint32(56, true), 9, 0xc33707d6);
    c = gg(c, d, a, b, buffer.getUint32(12, true), 14, 0xf4d50d87);
    b = gg(b, c, d, a, buffer.getUint32(32, true), 20, 0x455a14ed);
    a = gg(a, b, c, d, buffer.getUint32(52, true), 5, 0xa9e3e905);
    d = gg(d, a, b, c, buffer.getUint32(8, true), 9, 0xfcefa3f8);
    c = gg(c, d, a, b, buffer.getUint32(28, true), 14, 0x676f02d9);
    b = gg(b, c, d, a, buffer.getUint32(48, true), 20, 0x8d2a4c8a);

    a = hh(a, b, c, d, buffer.getUint32(20, true), 4, 0xfffa3942);
    d = hh(d, a, b, c, buffer.getUint32(32, true), 11, 0x8771f681);
    c = hh(c, d, a, b, buffer.getUint32(44, true), 16, 0x6d9d6122);
    b = hh(b, c, d, a, buffer.getUint32(56, true), 23, 0xfde5380c);
    a = hh(a, b, c, d, buffer.getUint32(4, true), 4, 0xa4beea44);
    d = hh(d, a, b, c, buffer.getUint32(16, true), 11, 0x4bdecfa9);
    c = hh(c, d, a, b, buffer.getUint32(28, true), 16, 0xf6bb4b60);
    b = hh(b, c, d, a, buffer.getUint32(40, true), 23, 0xbebfbc70);
    a = hh(a, b, c, d, buffer.getUint32(52, true), 4, 0x289b7ec6);
    d = hh(d, a, b, c, buffer.getUint32(0, true), 11, 0xeaa127fa);
    c = hh(c, d, a, b, buffer.getUint32(12, true), 16, 0xd4ef3085);
    b = hh(b, c, d, a, buffer.getUint32(24, true), 23, 0x04881d05);
    a = hh(a, b, c, d, buffer.getUint32(36, true), 4, 0xd9d4d039);
    d = hh(d, a, b, c, buffer.getUint32(48, true), 11, 0xe6db99e5);
    c = hh(c, d, a, b, buffer.getUint32(60, true), 16, 0x1fa27cf8);
    b = hh(b, c, d, a, buffer.getUint32(8, true), 23, 0xc4ac5665);

    a = ii(a, b, c, d, buffer.getUint32(0, true), 6, 0xf4292244);
    d = ii(d, a, b, c, buffer.getUint32(28, true), 10, 0x432aff97);
    c = ii(c, d, a, b, buffer.getUint32(56, true), 15, 0xab9423a7);
    b = ii(b, c, d, a, buffer.getUint32(20, true), 21, 0xfc93a039);
    a = ii(a, b, c, d, buffer.getUint32(48, true), 6, 0x655b59c3);
    d = ii(d, a, b, c, buffer.getUint32(12, true), 10, 0x8f0ccc92);
    c = ii(c, d, a, b, buffer.getUint32(40, true), 15, 0xffeff47d);
    b = ii(b, c, d, a, buffer.getUint32(4, true), 21, 0x85845dd1);
    a = ii(a, b, c, d, buffer.getUint32(32, true), 6, 0x6fa87e4f);
    d = ii(d, a, b, c, buffer.getUint32(60, true), 10, 0xfe2ce6e0);
    c = ii(c, d, a, b, buffer.getUint32(24, true), 15, 0xa3014314);
    b = ii(b, c, d, a, buffer.getUint32(52, true), 21, 0x4e0811a1);
    a = ii(a, b, c, d, buffer.getUint32(16, true), 6, 0xf7537e82);
    d = ii(d, a, b, c, buffer.getUint32(44, true), 10, 0xbd3af235);
    c = ii(c, d, a, b, buffer.getUint32(8, true), 15, 0x2ad7d2bb);
    b = ii(b, c, d, a, buffer.getUint32(36, true), 21, 0xeb86d391);

    state[0] = (a + state[0]) & 0xffffffff;
    state[1] = (b + state[1]) & 0xffffffff;
    state[2] = (c + state[2]) & 0xffffffff;
    state[3] = (d + state[3]) & 0xffffffff;
  }

  reset(): void {
    this.state = Uint32Array.from(INIT);
    this.buffer = new DataView(new ArrayBuffer(BLOCK_SIZE));
    this.bufferLength = 0;
    this.bytesHashed = 0;
    this.finished = false;
  }
}

function cmn(q: number, a: number, b: number, x: number, s: number, t: number) {
  a = (((a + q) & 0xffffffff) + ((x + t) & 0xffffffff)) & 0xffffffff;
  return (((a << s) | (a >>> (32 - s))) + b) & 0xffffffff;
}

function ff(a: number, b: number, c: number, d: number, x: number, s: number, t: number) {
  return cmn((b & c) | (~b & d), a, b, x, s, t);
}

function gg(a: number, b: number, c: number, d: number, x: number, s: number, t: number) {
  return cmn((b & d) | (c & ~d), a, b, x, s, t);
}

function hh(a: number, b: number, c: number, d: number, x: number, s: number, t: number) {
  return cmn(b ^ c ^ d, a, b, x, s, t);
}

function ii(a: number, b: number, c: number, d: number, x: number, s: number, t: number) {
  return cmn(c ^ (b | ~d), a, b, x, s, t);
}

function isEmptyData(data: SourceData): boolean {
  if (typeof data === "string") {
    return data.length === 0;
  }

  return data.byteLength === 0;
}

function convertToBuffer(data: SourceData): Uint8Array {
  if (typeof data === "string") {
    return fromUtf8(data);
  }

  if (ArrayBuffer.isView(data)) {
    return new Uint8Array(data.buffer, data.byteOffset, data.byteLength / Uint8Array.BYTES_PER_ELEMENT);
  }

  return new Uint8Array(data);
}
